Hulls for boats, ships and other watercraft are known for planing on water at higher speeds and for water displacement at lower speeds. A wide variety of water surface conditions exist in which the hulls must safely plane as well as displace water. Typical water surface conditions include flat, smooth surfaces associated with protected bays and inlets, choppy waves found in open bays, and smooth or choppy swells in offshore ocean areas. Hulls designed to provide safe and comfortable transportation under one set of water conditions may be unsafe and uncomfortable when used under conditions different from those for which the hull was primarily designed.
For planing on water, a popular hull design for powerboats is a “V” configuration. The V configuration represents a compromise between lateral stability, such as may be achieved with a catamaran or flat bottom design, and a need to avoid excessive bouncing or “pounding” that occurs when a flat or rounded bottom vessel is propelled at higher planing speeds over a moderately choppy water surface. One drawback in most planing designs is that a wide forward arrangement may tend to act as an airfoil as the speed of the hull increases. The wide forward arrangement causes the hull to generate excessive lift in a forward portion of the vessel. This lift produces the up and down motion commonly known as “porpoising.” The porpoising phenomenon is exacerbated in rough or choppy water in which the hull may be given an initial upward lift by a wave or swell, may be further lifted by the aerodynamic force of the air and, after reaching a maximum height, will fall back to the water surface to crash against the next wave. Such pounding is not only uncomfortable to passengers but may dangerously stress structural components of the vessel.
Where high-speed operation is desired, a deepening and narrowing of the V configuration is helpful in reducing the aerodynamic tendency of the hull to act as an airfoil and become airborne over the water surface.
The deep V also helps to part the water, resulting in a lessening of the pounding of the hull as it meets the water. A deep V with a 24-degree dead rise at a transom of the boat permits a softer water entry when the boat lands after leaving the water. Sharpening and lightening the forward arrangement for water entry may increase these advantages. Nearly all modern ocean-running, high-performance hulls include these features.
Further deepening of the V will ameliorate the vertical motion of the forward part of the hull, providing greater longitudinal stability while continuing to reduce the porpoising phenomenon. However, such benefits are gained at the expense of lateral stability. Further, the deep V hull has a natural tendency to rock and roll in moderate seas at slow speeds or while drifting. This places a practical limit upon the angle of the V that a hull may have without sacrificing comfort or safety.
Various tests suggest another V-hull drawback in which a greater power setting requiring a peak energy expenditure is required to overcome drag and hydroplane the conventional V-hull powerboat. Details of such tests are found in Powerboat Reports, August-November 2002, Belvoir Publications, Inc., Greenwich, Conn.
In sharp contrast to deep V configurations, catamaran and flat bottom hull are designed for displacing water at slower speeds. Such designs may incorporate a right-angle hard chine at or near the water surface. These flat bottom designs are exceptionally stable against lateral rolling, but because they lack the features of a V or deep V configuration, they are not well suited for high-speed travel, especially in rough water conditions.
A transition hull suitable for both planing a watercraft at higher speeds and for displacing water at lower speeds under most water surface conditions is needed.